DME is sent 6 weeks prior to check in (which means most get it 38-40 days out.)
But, you don't really need the DME yellow tags at all to make full use of the service.
You can just go to the DME welcome desk and provide them with the regular airline claim check numbers and DME will go to baggage claim and deliver the luggage to your room.
If you'd like to check to see if DME is expecting your arrival...
Call Disney's Magical Express Guest Services at (866) 599-0951.
They have always been extremely nice and very helpful to me.
I always receive my magic bands well before my luggage tags.
Also, if you are using a travel agent, I am pretty sure that the bands come straight from Disney while the rest pass through the travel agency first so there is an additional delay.